Formation pathways of the compact stellar systems

TL;DR

This study investigates the origins of compact stellar systems using simulations, revealing diverse formation pathways including starbursts, tidal stripping, and intrinsic formation, with differences based on environment and history.

Contribution

It provides a detailed simulation-based analysis of CSS formation pathways, distinguishing between stripped and intrinsically formed objects, and their environmental dependencies.

Findings

Most CSSs form from short starbursts.

Sixteen CSSs result from tidal stripping.

Intrinsic CSSs differ in age and metallicity based on their environment.

Abstract

The formation pathways of compact stellar systems (CSSs) are still under debate. We utilize the \NH\ simulation to investigate the origins of such objects in the field environment. We identified 55 CSS candidates in the simulation whose properties are similar to those of the observed ultra-compact dwarfs and compact ellipticals. All but two most massive objects (compact elliptical candidates) are a result of a short starburst. Sixteen are formed by tidal stripping, while the other 39 are intrinsically compact from their birth. The stripped objects originate from dwarf-like galaxies with a dark halo, but most of their dark matter is stripped through their orbital motion around a more massive neighbor galaxy. The 39 intrinsically compact systems are further divided into ``associated'' or ``isolated'' groups, depending on whether they were born near a massive dark halo or not. The isolated intrinsic compact objects (7) are born in a dark halo and their stellar properties are older and metal-poor compared to the associated counterparts (32). The stripped compact objects occupy a distinct region in the age-metallicity plane from the intrinsic compact objects. The associated intrinsic compact objects in our sample have never had a dark halo; they are the surviving star clumps of a massive galaxy.